[New cytogenetic classification of precancerous lesions and carcinomas of the endometrium: possibilities and limits of immunohistochemical differentiation].

Various grades of adenomatous hyperplasia represent precancerous states leading to the most common type of adenocarcinoma with endometrial differentiation. Grades 1 and 2 are characterized by architectural abnormalities only (complex hyperplasia). They rarely progress to carcinoma. Grade 3 in addition is characterized by cytological atypicalities (atypical hyperplasia) and shows a much higher progression rate into invasive carcinoma. Endometrial carcinomas may originate from endometrial glandular epithelium and show endometrial differentiation, or from various types of metaplasias developing in the endometrium from pluripotent Müllerian epithelium. They then show endocervical or serous papillary differentiation. Because of their differences in spread, speed of growth and survival rates, it is important to subclassify these endometrial carcinomas. Immunohistochemically, adenocarcinomas with endometrial differentiation including adenoacanthomas and adenosquamous carcinomas can be recognized by their coexpression of cytokeratin 8 and vimentin, and by their negative reaction for CEA. Distinction from adenocarcinomas with mucinous differentiation, including muceopidermoid adenocarcinomas, is possible by their negative reaction for vimentin and by their positive reaction for CEA. On the other hand, carcinomas with mucinous differentiation primarily located in the endometrium can not be distinguished from those primarily located in the endocervix by immunohistochemistry; that distinction must be made topographically. The same holds true for clear cell carcinomas of both locations. Over the past decade, mucinous adenocarcinomas and clear cell carcinomas originating from the endometrium have increased, whereas adenocarcinomas with endometrial differentiation have become less frequent. This shift is closely related to the altered postmenopausal hormone substitution with the addition of the synthetic gestagens. These apparently stimulate proliferation of endocervical epithelium not only in the endocervix, but also that arising in endocervical metaplasias of the endometrium.